Despite the availability of potent HIV antiviral therapies, there exists a continuing need to identify and develop new drugs that inhibit the replication of the human immunodeficiency viruses, the causative agents of AIDS. Recent studies in our laboratory and others have characterized the mechanism of action of the small molecule maturation inhibitor 3-O-{3',3'-dimethylsuccinyl}-betulinic acid (DSB). DSB is a potent and highly selective inhibitor of HIV-1 replication that acts by specifically interfering with cleavage of the CA-SP1 site in Gag during viral maturation, resulting in incompletely matured particles that are poorly infectious. Our recent studies have shown that DSB binds specifically to immature HIV-1 particles, and this binding was correlated with HIV-1 sensitivity to DSB antiviral activity. The identification of the CA-SP1 cleavage site as an HIV-1 vulnerability to a small molecule inhibitor, coupled with the observation that antiviral activity is linked to DSB binding, suggests that additional molecules that inhibit HIV-1 maturation may be identified by screening for compounds that competitively inhibit DSB binding to immature HIV-1 particles. In this R21 application, we propose to capitalize our expertise in HIV-1 molecular biology and our new understanding of the DSB antiviral mechanism to develop a rapid SPA-based assay for the binding of DSB to immature HIV-1 pseudovirions. Once the assay has been established, we will further optimize and adapt the system for application to high throughput molecular screening of large compound libraries to identify molecules that inhibit the interaction as potential leads for the development of novel HIV-1 maturation inhibitors.